The present invention relates to the field of substrates, and more particularly, to the field of using absorbing materials in substrates, the substrates being coupled together by a means for cohering or like means for cohesively laminating so as to significantly decrease or eliminate water or like liquid buildup or condensation between the coupled substrates.
Liquid crystal display (LCD) devices are well known in the art and are useful for many applications in numerous industries (such as, for example, the avionics, consumer goods and the computer industries). Several types of LCD substrates are in production. The manufacture of LCD substrates typically require capturing a thin layer of liquid crystal between two pieces of transparent substrates, such as glass or plastic, forming a liquid crystal cell. When an electric field is applied, the field alters the molecular alignment of the liquid crystal, thus affecting the light that is passed through the crystal. This phenomena turns small windows of light known as pixels (picture elements) xe2x80x9conxe2x80x9d and xe2x80x9coff.xe2x80x9d LCD displays are usually light-weight, require low power and provide precise viewing resolution. Further, LCD displays are now manufactured as rigid substrates or flexible substrates.
The liquid crystal must be in a particular orientation, or oriented in the correct direction, to operate properly. The orientation of the liquid crystal is achieved in the manufacturing process by rubbing the two plates with a polymer, creating parallel furrows. The most common type of LCD on the market today is a passive form in which all the pixels in each row are tied together, thus reducing the need to control each pixel independently. But, that means the pixels remain in a state between on and off, resulting in a loss of contrast. It also produces annoying ghost images, especially of moving objects, in either the rigid substrate or the flexible substrate form.
Researchers have been struggling for years to develop cost-efficient active displays in which each pixel is controlled by its own transistor. Active matrix displays are now available on laptops, but they are expensive to manufacture, partly because the transistors can be so easily damaged during the fabrication of the display screen. Some technologies not currently on the market could potentially reduce the cost, including ferroelectric liquid crystal cells (in which a thin film transistors would be used to control the pixels individually). In a ferroelectric screen, each pixel would be either on or off, thus producing an image that is light and dark, like the numbers on a digital watch.
Fabrication of LCD displays has proven extremely difficult, often resulting in low yields and thus, higher costs. When the polymer is rubbed across the film of transistors to provide alignment for the liquid crystal, it may cause mechanical damage and electrostatic charges that can potentially damage the transistors. The yield of the transistors then decreases drastically, which affects the price of the finished LCD display substrate. And, because of the sensitivity of such screens, the screens must be protected, usually by adhering another substrate (such as a glass cover of equivalent dimensions) to the LCD substrate. Moreover, another advantage of employing another substrate is that it increases optical performance. An optical coating (such as an anti-reflective coating) may also optionally be coated on to the substrate which is coupled or otherwise adhered to the LCD display.
One method of adhering a protective substrate to the LCD cell (active and passive plate combination) is known as the xe2x80x9cgravity pourxe2x80x9d method. In this method, a clean LCD cell is placed immediately adjacent to a clean protective substrate at a 90 degree vertical angle so that the LCD substrate and the protective substrate are parallel to each other and in close proximity to each other. Bond tape (such as VHB high bond tape manufactured by Minnesota Mining and Manufacturing), similar to double-sided tape, is then applied to the periphery edges of the LCD substrate (typically within 0.060 inches from the outer periphery). The LCD substrate with cover glass attached is preferably oriented at approximately 90 degrees from horizontal. Then, the two substrates are precisely brought together so that the bond tape provides a seal between the periphery edges of the two substrates. In this construct, an air gap or air cell is created between the two substrates of known width (usually 0.025 inches to 0.045 inches apart, which are the typical commercial widths available for bond tape). Then, silicone or another like optical coupling material is poured between the two substrates along an opening in the top edge of the tape-bonded substrates and allowed to slowly permeate between the substrates by gravitational forces. Another opening (usually also located at the top edge) is also required to allow the air volume to escape from the air gap as the pour process continues. This gravitational pour process usually takes more than an hour and may or may not be successful in completely filling the entire air gap between the bonded substrates. The viscous fluid typically employed has a characteristic viscosity of about 150 cps, but can go as high as 4500 cps.
The problems associated with using the pour prior art adhesion process, however, are numerous. First, adhesive optical materials bond the substrates together to form an almost permanent, rigid planar beam. And, for example, filling all the air cell space between the two substrates is difficult due to the viscosity of the adhesion fluid which often leads to visible air volume space or air bubble formation between the substrates. Further, this process is slow, which means that unless the timing is precise for the complete permeation of the air gap with fluid, those optical fluids which undergo a chemical cure will do so before the substrate adhesion process is complete (since most viscous fluid pot life is in the range of 15 minutes to 1 hour). Thus, if the fluid cures too quickly before the gravity pour process is complete, it may require repeated pour processes, unusable substrates, partially bonded substrates or damaged substrates. The position of the substrates at 90 degrees also introduces substantial friction between the two substrates, which reduces the even flow of viscous fluid between the substrates during the injection process. And, because the gravity pour method results in inconsistent permeation, the final substrate does not always possess uniformity of throughout the substrate. Moreover, other manufacturers in the art have used fluids or UV cured adhesives or optical epoxies to optically couple substrates, however the gap between the substrates is very small as to transmit the axial deflection directly to the LCD substrate, which causes optical distortions which can persist. Finally, if the gravity pour process is not executed precisely under careful conditions, the two substrates, after bonding, sometimes exhibit a bowl shape in the middle of the substrates due to increased hydrostatic pressure, leading to an unusable LCD substrate.
U.S. patent application Ser. No. 09/410,888 commonly-owned by the assignee of the present invention, discloses a novel method for optically coupling substrates together. The two substrates are then sealed adjacent to each other by a means for sealing. A means for optically coupling (such as an optically clear fluid) is then de-gassed to remove any dissolved or remaining gas within the means. Then, a pressurized means for injecting (such as a pressurized syringe) is filled with the de-gassed means for optically coupling, while a means for exhausting the means for optically coupling is provided through the means for bonding along a top edge of the bonded substrates. The method requires providing two clean substrates and positioning each at approximately a 20 degree angle (or an incline of various ranges) parallel to each other and in close proximity to each other. The pressurized means for injecting then introduces, through the means for sealing, the means for optically coupling between the two substrates from a side peripheral edge. The means for optically coupling is subsequently allowed to permeate throughout the entire air cell area, and then, cured or allowed to cure. One advantage of this method is that it allows for higher yields of coupled substrates. And, due to the gel-like characteristics of the means for optical laminating employed, improperly injected coupled substrates can be taken apart and remanufactured according to the method disclosed. Without such a method, damaged coupled substrates were usually discarded even if the LCD substrate was in good operating condition because the prior art optical lamination would cure to a hard adhesive consistency.
While U.S. patent application Ser. No. 09/410,888 discloses a novel method for coupling substrates together by the injection of a degassed means for optically coupling, it has been discovered that under certain temperature ranges and environmental conditions, small water (or other liquid) droplets have the capability to permeate the means for sealing (such as, for example, the RTV seal surrounding the substrate edge) and thus, be introduced into the means for optically coupling resulting in a condensation-like appearance of the bonded substrate. While the cause of this condensation-like phenomena is not clear, it has been suggested that a preferred means for optically coupling (e.g. Q3-6575 manufactured by Dow Corning or like dielectric material) is hydrophobic, meaning that it does not absorb liquid (such as, for example, water), but will allow the liquid to transmit through the means for optically coupling if present in sufficient quantities (such as, for example, during high humidity conditions). If this occurs, the view of the coupled substrate appears hazy due to the small liquid droplets which have permeated portions of the means for optically coupling. The water droplets also result in significantly increased diffuse reflectance. This phenomena is exhibited, for example, when two glass substrates are subjected to the method of application Ser. No. 09/410,888. During the humidity test of this method, it was discovered that subjecting clean glass plates (i.e., glass plates without any absorbing material, polarizer or like material applied to either substrate) to this method resulted in the hazy view, despite efforts to remove the haze with conventional cleaning solutions. This result was unexpected because products manufactured by the method disclosed in application Ser. No. 09/410,888 never exhibited this phenomena. However, these products had not been tested under various temperature ranges and environmental conditions. Detailed inspection of the test substrates revealed small portions of liquid permeated through the edge seal gasket of the air cell into the coupling material. What is thus required is a method of using absorbing material or a like means for absorbing in the coupling substrate process to significantly decrease or eliminate liquid buildup between the coupled substrates.
Those of skill in the art recognize that polarizers and polarizing films are designed to transmit light waves along one axis and absorb them on another. Polarizers are applied on each side of every LCD substrate. The axes of the polarizers are crossed at 90 degrees, so that the light absorbing and light transmitting axes are oriented at 90 degrees to each other. Standing alone, polarizers crossed in this manner do not allow light to pass. However, in the power off state, the liquid crystal cells in the LCD panel between the crossed polarizers rotate light passing through them 90 degrees, defeating the effect of the crossed polarizers and causing the display to appear transparent. When the surface of an individual liquid crystal cell in the LCD panel is electrically charged or activated, the cell ceases to rotate the polarized light and the segment appears as a dark spot on the screen. By electronically controlling the activation state of the individual cells in the LCD panel, information can be displayed.
Polarizing films for LCD applications are usually constructed of a stretched film of polyvinyl alcohol (PVA) which is then soaked with an iodine solution. The iodine diffuses into the PVA and forms a complex compound within the coils of the long chains of the host. As a result of the dichroic nature of iodine, the material absorbs most of the visible light polarized parallel to the length of the chains but transmits the light polarized perpendicular to the chains.
In general, materials used to construct absorbing or polarizing films such as PVA film characteristically absorb liquid such as water, however, excessive amounts of moisture absorption can be detrimental to the performance of the polarizer because the iodine may leach out of the material. Testing has shown that if the edges of the polarizer are properly sealed, polarizer films are able to absorb small amounts of moisture without a reduction in performance. This moisture absorption is adequate to eliminate the development of condensation within optical coupling gels.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The present invention is a method of using films, polarizers, means for absorbing or like absorptive materials in coupling substrates together. The method requires providing two clean substrates, applying a means for absorbing to at least one of the substrates"" surface which will face the other substrate, and positioning each substrate parallel to each other and in close proximity to each other. The two substrates are then sealed adjacent to each other by a means for sealing, with the means for absorbing located therebetween. A means for optically coupling (such as an optically clear gel) is then de-gassed to remove any dissolved or remaining gas within the means. Then, a pressurized means for injecting (such as a pressurized syringe) is filled with the de-gassed optical laminate means, while a means for exhausting the optical laminate means is provided through the means for bonding along a top edge of the bonded substrates. The pressurized means for injecting then introduces, through the means for sealing, the means for optical laminating between the two substrates from a side peripheral edge. The means for optically coupling is subsequently allowed to permeate throughout the entire air cell area, and then, cured or allowed to cure. By employing the means for absorbing within the coupled substrates, liquid introduction into the means for optically coupling, and thus the air cell, is significantly decreased or eliminated.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.